The SA1 communicates at 9600,N,8,1 serial settings. Each command begins with a * and terminates with a <CR>. <CR><LF> is also acceptable. Here are a list of commands:
*I<CR> or *i<CR> returns the string "SWR METER". Used by the Windows app to find the SA1
*F?<CR> or *f?<CR> returns the current frequency setting of the FA1 in MHz
*Fnnnn<CR> or *fnnnn<CR> Sets the frequency of the SA1 to nnnn kHz, all non-numeric characters are ignored.
*S?<CR> or *s?<CR> returns the current SWR reading on the SA-1
The application was written in PureBasic. You can download a free version from the PureBasic website and modify the app as you see fit. There are versions for Linux and MacOS so it may be possible to compile the app for other platforms besides Windows.